Iron oxide pigments and process of producing the same as by-products of the reduction of aromatic nitrocompounds



Patented M... 15, 1932 UNITED STATES PATENT OFFICE .nrmus UK, or unnnmonn/nmnnnmm, smut, assronon. To '1. o. rmnnnmuszmm mrmwnsnnnsonm, or rnamoM-on-rnn-nan r, GERMANY, A

ooarom'rlon or exam IRON OXIDE PIGKENTS AND PROCESS OI PBODUCIHGI'HE ELIE A8 BY-PRODUCTS THE REDUCTION OF'LROIATIC NITBOCOHPOUNDS in Drawing. Application ma August 1:, 1m, Serial no. 885,467, and in Germany lay a, 1m.

' Thgdpresent invention relates to a process of pr ucmg ll'OIl oxide pigment-s; more specifically it relates .to a process in which a finely divided iron oxide is obtained as a 5 by-product from the reduction of aromatic mtro compounds to the. corresponding amines by means of iron and acid or an acid reacting salt. The invention also embraces the resulting new products.

In the methods of producing aromatic amines from aromatic nitro compounds heretofore known and used for a long time involving the use of iron and an amount of '2 This oxide is not useful as a color pigment and is of very inferior quality on account oi its slight coloring and covering power.

To illustrate the old process it may be stated that in the manufacture of aniline 25 with every 100 parts of nitrobenzene about a 100 parts of iron, 8 to 10 parts of concentrated hydrochloric acid (specific gravity 1.16) and about 100 parts of water are emloyed. The reduction is carried out by add- 1n the nitrobenzene and iron to the hydroch oric acid and water heated to about 100 at such a rate that the temperature of about 100 C. is maintained by the heat of reaction.

When reduction is finished, the oily layer p 35 of aniline is drawn oil and the remainmg aqueous liquid distilled by steam after having added some lime, if necessary. The iron oxide represents a waste product of no commercial value. As is further, known, the hydrochloric acid employed in the reduction may be substituted by a more or less equivalent quantity of sulfuric acid, acetic acid, sulfurous acid or the like or by a dilute solution i. e. an aqueous solution containing less 4 than 5 percent of a salt exerting an acid reaction due to h drol sis such as ferrous chloride without 0 angm the properties of the resulting iron oxide udge.

' According to this invention the reduction 1s carried out under such conditions that the aqueous phase of the reaction mixture is a highly concentrated salt solution, that is, an

aqueous solution which contains at least 12 percent of a dissolved salt, preferably 15 to percent and the concentration of which may rise as far as the saturatin concentration of the respective salt and oes not fall below the lower limit of 12 percent during the reduction process. This is efiected by 'addmg enough of an easily soluble salt to the amount, required for reduction, of the dilute ac d or dilute solution of a salt exerting an acid reaction due to h drolysis, so that a solution of the desired 111 h concentration results', or, what in practlce amounts to the same thing, by dissolving the acid or acid salt, as the case may be, in a concentrated aqueous solution of a salt instead of in water. In other words, the acid reacting salt, or the mixture of acid and salt, as the case may be, is used in such amount and concentration as to produce a ferroso-ferric oxide sludge substantiallyfree from acidic residues and adapted to form a black commercial iron oxide pigment. The salts which have been found suitable for carryin out my process are of difi'erent kinds. he easily soluble chlorides of such metals as are more electroositive than iron, for example, the chlorides of alkali and alkaline earth metals, of ma nesium, of zinc and aluminium preferab y are used; but easily soluble salts of other acids or other metals and especially the salts 'of'iro'n itself have been likewise found efiicaacids, are operative, and the salts of ammonia or amines and those of organic acids do not difier anyhow from others in their efiect.

addition of an acid may be dispensed with.

'This hydrolysis largely depends on the composition of the salt and the action of the salt upon the iron i. e. the reducing effect is different in accordance therewith. A certain minimum degree of hydrolysis, therefore, must be present in the aqueous phase of the reaction mixture and I have found that generally 2 to 3 parts of the acid reacting salt upon 100 parts of nitro compound will suflice to produce a sufiicient hydrolysis. Examples for salts of this kind are those easily soluble and acid reacting salts of metals more electropositive than iron such as zinc chloride especially the acid reacting salts of iron itself, and the salts of aromatic amines e. g. aniline hydrochloride or aniline acetate.

The characteristic feature of the new process is in every case that the nitro compound to be reduced is treated with iron and a concentrated aqueous solution of a'salt, which besides ions of the salt contains also free hy-' drogen ions, the latter, however, being in such a small amount as is insufficient to dissolve the iron, or in other words the quantity of acid in the reduction mixture does not substantially differ from that used in the old process referred to above. It therefore 1s distinguished from the old method by the fact that the concentration of the solution of the salt is much higher than hitherto used i. e. it always exceeds 12 percent and preferably solutions of 20 percent or more content in salt-are employed. If the reduction is carried out in the presence of such concentrated salt solution which besides the ions of the respective salt contains also free hydrogen ions (the process not essentially departing in other respects from the customary processes-as will be evidenced by the examples set forth) there remains after the separation of the aromatic amine, for example, aniline resulting from the nitro compound a slurry which contains the oxidlzed iron in a most finely divided state. and, in fact, in most cases as a deep black ferrosofer: ric oxide Fe O and in certain'cases as a yellow brown hydrate of the iron oxide Fe p After levi ation, washing out and drying this oxide is useful asa color pigment either directly or, ii red shades are desired, after being subjected to a preliminary calcination.

The process is illustrated by the following examples (the parts being by'weight). It will be understood that it is capable of being carried out by other nitro compounds than those mentioned in these examples, for exsalts of rare earth metals can be em loyed instead of the salts mentioned in the examples, if only they are soluble enough to give the necessary high concentration. Other acids such as acetic acid, sulfonic acids can be used andeven nitric acid is operative.

Examples 1. 150 parts of a 30% sodium chloride solution is made acid with 15 parts of 1,16 sp. gr. hydrochloric acid, and treated with 250 parts of'ground iron. At 100, 200 parts of nitrobenzene are allowed to run in in such a way that the temperature maintains itself at 100 due to the heat of reaction. When the reduction is finished, the resulting aniline is separated in the well-known manner. There remains behind a highly valuable deep black ferroso-ferric oxide which is purified from the salts and dried, The ferroso ferric oxide so obtained in contrast to that produced by the reduction methods heretofore known is capable of being easily converted into a red iron oxide pigment by calcination and oxidation. I

2. The process is carried out as described in Example 1 except that 150.parts of a 40% calcium chloride solution is used in place of the 150 parts of sodium chloride solution.

3. 180 parts of iron powder are introduced at 100 C. during the course of several hours into a mixture of 150 parts of water, 200-parts of nitrobenzene, 60 parts of calcium chloride, and 6 parts of 1.16 sp. gr. hydrochloric acid. When the reaction is finished, the aniline is obtained in the well-known manner, the slurry remaining behind is washed out, and calcined at 700 C. A very valuable red iron oxide of good coloring power is obtained.

4. 20 parts ofhydrochloric acid (specific gravity 1.16) and 250 parts of iron turnings are added to 190 parts of a 30% magnesium chloride solution. This mass is heated and 200 parts of a-nitronaphthalene vare introduced into it slowly. When the reduction is finished, the ready a-naphthylamine is separated in the well known manner. The resulting very valuable ferroso-ferric oxide is washed and dried as in the previous examples.

5. 200 parts of o-nitro-toluene in a solution of 20 parts of aluminum chloride and 30parts of sodium chloride in 200 parts of water are reduced in the usual manner by means of 220 parts of iron and parts of 1.16 sp. gr.hydrochloric acid. After working up, besides \o-toluidine a yellow-brown iron oxide is obtained which is transformed into a deep red iron pigment on heating.

6. 485 parts of water 240 parts of rock salt 115 parts of sulfuric acid 78% 300 parts of ground iron are-stirred and heated at 100 G. 'Then 500 arts of ground iron and600 parts of nitronzene are allowed to slowly run into the mixture. After complete reduction the ani-' line is separated in the known manner and the remaining slurry .levigated; washed out and dried. A black iron oxide pigment is. obtained having a very high coloring power and being converted into aredviolet iron oxide by calcining it.

7. 150 parts of water 60 parts of magnesium sulfate parts of formic acid 80% are heated to 100C. and

300 parts of ground iron 200. parts of nitrobenzene 100 parts of water added to' the mixture in small portions.

9. 150 parts of water 50 parts of sodium acetate 30 parts of hydrochloric acid 20 B. 250 parts of iron borings are heated at 100 C. and

200 parts of nitrobenzene and 50 parts of water allowed to slowly run into the mixture. After separation of the aniline a brown black slurry of very fine texture remains which is con- 7 verted into a bright red iron oxide by calcining it.

10. 7 5 parts of water 50 parts of ammonium bromide parts of hydrobromic acid 40% are heated to 100 C. and

250 parts of ground iron and 200 parts of nitrobenzene added in small portions. The working up of the. reactionmixture yields a deep black iron oxide pigment which can be converted into a lustrous red iron oxide.

11. 150 parts of water 40 parts of ammonium chloride I 30 parts of hydrochloric acid 35% are heated at 100 C. and

250 parts of ground iron and 200 parts of a-nitronaphthalene added to the mixture. If the mixture should become too stifi in the course of the reduction, a small quantity of water maybe added. After complete reduction the a-naphthylamine is extracted by means of a solvent and the slurry worked up as shown above. A bluish 79 black iron oxide fpigment is obtained.

12. 100 parts 0 aniline water (an a ueous solution containingabout 3 ercent aniline). 291 parts of a ferrous chlori e solution (spe- 'cific gravit 1.41), 70 parts of a 35% hydrochloric aci and 40 parts of nitrobenzene are 7 heated to about 100 G. Then 560 parts ofnitrobenzene and 780 parts of finely ground iron are added at such a rate that the temperature of about 100 C. is maintained due to the'heat of reaction. When'reduction is fin- I ished, a deep black ferroso-ferric oxide is obtained after purifying the slurry remaining behind as shown in the foregoing examples. By calcining it a red iron oxide of, bluish shade and of high coloring power is produced.

13. 100 parts of water, 40 parts of sodium nitrate, 24 parts of concentrated sulfuric acid are heated to about 100 C. At this temperature 250 parts of finely ground iron and a mixture of 180 parts of nitrobenzene and 40 parts of water is introduced at such a rate that the temperature of about C. is maintained due to the heat of reaction. The work- 95 ing up as shown in the foregoing examples yields a bluish black iron oxide pigment which is converted to a red iron oxide of violet shade by calcining it.

14. 250 parts of ground cast iron turn- 10. ings are added to parts of a 20% ferrous chloride solution and 200 parts of o-nitrotoluene are allowed to slowly run in at boiling temperature. When reduction is finished,

' the o-toluidine is obtained in the known man- 106 ner. The iron slurry remaining behind is freed from unattacked iron and soluble salts by means of levigationand washing out and then dried. It represents a ferroso-ferric oxide of deep black color and high coloring and covering power.

15. 100 parts of water 21 parts of anhydrous ferric chloride 250 parts of iron borings are heated at 100 C. and

200 parts of o-nitrotoluene and 50-parts of water 0 allowed to slowly run into the mixture. After complete reduction the o-toluidine is separated and the remaining slurry yields after .levigating, washing out and drying a deep black color pigment having a high coloring power and being converted into a lustrous red 12 iron oxide by calcining it.

16. parts of water 50 parts of zinc chloride 250 parts of iron borings are heated to 100C. and 200 parts of nitrobenzene allowed to slowly run into the-mixture. After separation of the aniline a black iron oxide pigment havin a high color strength and a fine color sha e is obtained.

'17. 150 parts of water 100 parts of chrome alum 200 parts of nitrobenzene are heated at 100 C. and

to run into a 200 parts of a 30% magnesium chloride solution heated to about 100 C. and

containing about 200 parts of ground iron borings in such a Way that the temperature maintains itself at about 100 0. due to the reaction heat. lVhen reduction is finished,

the resulting aniline is separated in the known manner. The iron slurry remaining behind is purified as described in example 1 and thus yields a bluish black ferroso-ferric oxide of high coloring and covering power.

-' 19. 200'parts of nitrobenzene are allowedto run at 100 G. into a solution of parts of aniline hydrochloride in 150 partsof water containing about 180 parts of iron powder, in such a way that the temperature maintains itself at 100 C. due to the reaction heat. When reduction is finished, the resulting aniline is separated inthe known manner. There remains behind a highly valuable deep black ferroso-ferric oxide which is freed from unattacked iron and from soluble salts and then dried.

- .20. 200 parts of nitrobenzene and. 60 parts of'water are allowed to run into a mixture of 100 parts of water, 31 parts of aniline, 20 parts of glacial acetic acid and 250 parts of finelyv ground iron at about 100 C. The

' working up as shown in the foregoing examples yields a black iron oxide pigment of greyish shade which is converted to a brilliant yellowish red iron oxide by calcining it.

Thisis a continuation in part of my 00-- pending application Serial No. 106,929 filed May 5,1926.

I claim:

1. The process which comprises reducing an aromatic nitro compound with metallic iron and an acid-reacting concentrated aqueous solution of a salt insuflicient in' amount to dissolve the iron and in amount and concentration sufficient to produce a ferrosoferric oxide sludge substantially free from acidic residues and adapted to form a black commercial iron oxide pigment, separating the resulting ferroso-ferric oxide sludge from the resulting aromatic amino compound, and

purifying the former by washing. I

2. The process which comprises reducing ferric oxide sludge substantiall acidic residues and adapted to orm a com iron and an acid-reacting concentrated aqueous solution of a salt insuflicien't in'amount to dissolve the iron and in amount and concentration sufiicient, to produce a; ferrosofree from mercial ferrosq-ferric oxide pi ent,"separating the resulting ferrosoerric ox1de sludge from the resulting aromatic amino compound, purifying the'for'mer by levigation and washing, and drying and calcimng the resulting product.

3. The process which com rises reducing an aromatic nitro compoun with metallic iron and an amount of acid insuflicient to dissolve the iron, in the presence of a'concentrated aqueous solution of a salt, the acid and' salt being in amount and concentration suflicient to produce a ferroso-ferric ox1de sludge substantially free from acidic residues and adapted to form a commercial iron oxide pigment, separating the resulting ferrosoferric oxide sludge from the resulting aromatic amino compound, and purifying the former by Washing. 1

4. The process 'which comprises reducing an aromatic nitro compound with metallic iron and an amount ofacid insufiicient to dissolve the iron and under conditions of producing a ferroso-ferric oxide substantially free from acidic residues, in the presence of an aqueous solution containing at least 12 percent of adissolved salt, se aratin the resulting ferroso-ferric oxide s udge rom the resulting aromatic amino compound, and purifying the former by washing." l

5. The process which comprises reducing an aromatic nitro compound; with metallic iron and an amount of inorganic acid insuflicient to dissolve the iron and under conditions of producing a. ferroso-ferric oxide substantially free from acidic residues, in the presence of an aqueous solution containing, at least 12 percent of a salt of a metal, separating the resulting ferroso-ferric oxide sludge from the resulting aromatic amino compound, and purifying the former by washing.

' 6. The process which comprises reducing an aromatic nitro compound 7 with metallic iron and an amount of inorganic acid insufiicient to dissolve the iron, in the presence of an aqueous solution containing at least 12 percent of a chloride of a metal .more electropositive than iron, separating the resulting iron oxide sludge from the resulting aromatic amino compound, and purifying the former by wash-- ing. v

7. The process which comprises reducing an aromatic nitro compound with metallic iron and an amount of hydrochloric acidin- I sufficient to dissolve the iron, in the presence of an aqueous solution containing at least 12 percent of a dissolved chloride of a metal more electropositive than iron, separatin the resulting iron oxide sludge from the resu ting aromatic amino compound, and purifying the former by washing.

8. The process which comprises reducing a an aromatic nitro com oun with metallic iron and an amount of ydrochloric acid insufiicient to dissolve the iron, in the presence of a 30% solution of sodium chloride, separating the resulting iron oxide sludge from the' resultin aromatic amino compound, and purifying t e former by washing.

he process which com rises reducing an aromatic nitro com oun with metallic iron and a concentrate aqueous solution of a salt being capable of exerting an acid reaction in an aqueous solution under conditions of producing a ferroso-ferric oxide substantially freefrom acidic residues, the said salt being in amount and concentration suflicient to produce an iron oxide, sludge adapted to form a commercial iron oxide pigment, separating the resulting ferroso-ferric oxlde sludge from the resultin aromatic amino compound, and purifying the former by washmg. 7 10. The process which comprises reducing an aromatic nitro compound with metallic iron and an aqueous solution containing at least 12 per cent of an inorganic salt being capable of exerting an acid reaction in an aqueous solution under conditions of producing a ferroso-ferric oxide substantially free from acidic residues, separating the resulting I ironoxide sludge from the resulting aromatic amino compound and purifying the ferrosoferric oxide sludge by washing.

11. The process which comprises reducing an aromatlc nitro compound with metallic "iron and an aqueous solution containing at least 12 percent of a metal chloride being capable of exerting an acid reaction in an aqueous solution under conditions of producing a ferroso-ferric oxide substantially free from acidic residues, separating the resulting fer-- roso-ferric oxide sludge from-the resulting aromatic amino compound, and purifying the former by washing.

12. The rocess which comprises reducing an aromatic nitro compound with metallic iron and an aqueous. solution containing at least 12 percent of an iron chloride under conditions of producing a ferroso-ferric oxide substantialy free from acidic residues, separating the resulting ferroso-ferric oxide sludge from the resulting aromatic amino compound, and purifying the former by washing.

In testimony whereof, I afiix mg si ature JULIU L UX 

